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We have examined the complete longitudinal height velocity (HV) data of 135 (80 male and 55 female) chromosomally normal children from the Edinburgh Longitudinal Growth Study who were measured six-monthly between age 3 years and the onset of the adolescent growth spurt. Individual HV curves appeared to consist of a regular series of accelerations and decelerations in a cyclical fashion. After excluding variations due to measurement error, and basing the analysis on the pattern of acceleration, we were able to identify a number of spurts of regular occurrence. The mid-childhood spurt was clearly identified at ages 7.0 in boys and 6.7 years in girls, and could be identified in all children except one girl. Other spurts were also apparent; a pre-school spurt at ages 4.8 and 4.6, a late-childhood spurt at ages 9.2 and 8.6, and in children with an average-to-late onset of puberty, a prepubertal spurt at ages 10.8 and 10.0 years in boys and girls respectively. Synchronization at peak HV was performed for each spurt as described by Shuttleworth (1937) for the adolescent growth spurt. The overall pattern of growth appeared to be cyclical with a mean peak interval of 2.2 years in boys and 2.1 years in girls, the cycles appearing to continue until interrupted by the onset of the adolescent growth spurt. Sitting height velocity (SHV) and leg length velocity (LLV) curves also showed a cyclical pattern, but each varied independently. The magnitude of the HV spurts in an individual was dependent on the synchrony between the phases of SHV and LLV spurts. The cyclical pattern of prepubertal growth with its rapid changes in HV should be taken into account when assessing the growth of any child and in the response to any treatment offered.

Salivary testosterone (ST) levels were measured in 84 boys aged 7.3-16.2 from the Edinburgh Growth Study. The correlation coefficient between matched plasma/saliva samples was 0.88. Six samples were collected over the course of one day from 0900 to 2100 h each month in the majority of the children for 4 consecutive months. Mean daily ST levels showed a significant rise between each pubertal stage (genital (G) and pubic hair (PH]. The rise in ST became more rapid once a mean testicular volume (MTV) of 10 ml had been reached. The diurnal rhythm was assessed by individual curve fitting on the log scale and by cosinor analysis. A rhythm was present prepubertally and developed into a pattern similar to that of the adult rhythm by stage G3. The monthly rate of rise of ST was greatest at stage G4. A significant rise in ST levels was detectable immediately prior to an increase in MTV to 3 ml. This allowed earlier recognition of the clinical onset of puberty at testicular volume of 3 ml, which in this group occurred at 10.9 (SD 0.9) years. ST is a non-invasive and sensitive method for the serial monitoring of gonadal function in the prepubertal and adolescent boy.